Prior white-light and multicolor light emitting diode (LED) lighting color conversion processes involving inorganic phosphor powders waste a substantial portion of the photons from the LED due to light scattering, light trapping, and quantum yield conversion losses in most photoluminescent phosphor matrix structures. The high index of refraction and birefringence of many inorganic phosphor grains cause light scattering, preventing the majority of visible light from being emitted in the forward direction. Light scattering and light trapping within a color converter and LED combination is a problem associated with white LED lighting because it can lead to an overall waste of photons, as well as reduction in energy efficiency in a white light emitting LED lamp.
Moreover, some organic photoluminescent materials have exhibited very high conversion efficiencies with over 90% quantum yields, yielding high overall energy efficiencies for converted white-LEDs. However, after short periods of time after exposure to high intensity UV or blue light, these organic photoluminescent materials become increasingly transparent to blue light which results in an increase in transmitted blue light with a matched reduction in the emission spectrum.
Almost all organic and inorganic color conversion materials have exhibited broader than desirable color spectrum to be competitive with the color quality needed for high color range flat panel displays. Furthermore, light directionality of color converted lights has been limited by the omni-directional light emission characteristics of these color converters.
Thus, there is a need for a spectral color conversion apparatus and method that reduces light scattering and light trapping, improves quantum yield, provides choice of directionality of light, and increases the energy efficiency in white LED-lighting and the like, while still providing the potential for long luminance lifetime.